Wavelength Division Multiplexing (WDM) in optical networks has produced the need for improved optical laser sources. In such WDM networks, each fiber must transmit many wavelength channels, which are separated or combined at each node by special filters known as wavelength routers. A multiwavelength laser [1-4] is attractive for use as the optical source since it is capable of producing a large number of closely spaced wavelengths. (Note, the numbers in brackets refers to a reference listed in the Appendix.) By using a multiwavelength laser as a source, the destination of each channel can be changed by changing its wavelength. Prior art multiwavelength laser arrangements have used a transmissive grating [2-4], but when the wavelengths are very closely spaced the grating becomes impractical because of its size. It is then attractive to replace the transmissive grating [3] with a reflective grating [5], but, unfortunately, such a multiwavelength laser design exhibits unwanted resonances, caused by direct feedback and unwanted images, that must be eliminated.
What is needed is a multiwavelength laser having closely spaced wavelengths and reduced size and which does not exhibit unwanted resonances.